The present invention relates to a continuous commercial electrolytic process for the engrossment of wire and, in particular, to a method and an apparatus for the electrorefining or electrowinning of metals, particularly copper, by electrodepositing the metal onto a metal starting wire during the process.
The conventional method of producing copper wire used throughout industry starts with pure copper plates commonly named "cathodes" which are about 3.3 ft (1000 mm) square and about 5/8 inch (15 mm) thick. The cathodes are formed during electrorefining or electrowinning operations by electrodeposition of pure copper on thin starting sheets of refined copper or on a metal such as stainless steel from which the deposit is stripped. These starting sheets, also measuring about 3.3 ft square but about 0.04 inch (1 mm) thick, have to be intermittently introduced into the electrolytic tanks as the engrossed refined cathodic plates are removed as finished product, both operations using manual work. In addition, the electrolysis is generally carried out at low current densities which is defined as the amperage applied to the tanks spread over the immersed surface area of the total number of the cathodic starting sheets present (cathode current density), or expressed in terms of the wetted areas of the crude copper anodes being refined or inert anodes in electrowinning operations (anode current density). Low densities are generally inefficient since the quantity of copper deposited is directly proportional to the amount of current applied. Notwithstanding, higher current densities are not generally used in the present art to improve throughput and decrease the cost of producing a unit of copper as the quality of the plated metal thereby obtained in conventional tanks would be debased and/or the resulting roughness of the product become undesirable.
To manufacture wire the cathodes then have to be melted, cast and hot rolled in a separate and complex facility to produce rod which is normally 5/16 inch (7.94 mm) in diameter. This rod is then converted to wire, e.g., electrical wire. The first step in this process is the "rod breakdown" where the rod is cold drawn to about AWG #14. (1.628 mm). The intermediate wire after "rod breakdown" is further cold drawn to the final product size. During the cold drawing operation the wire must be periodically annealed.
Thus, the conventional method of copper wire production starting with an electrorefining or electrowinning process consumes much energy and requires extensive labor and capital costs. The melting, casting and hot rolling operations also subject the product to additional oxidation and potential contamination from foreign materials such as refractory and roll materials which can subsequently cause problems to the wire drawers generally in the form of wire breaks during drawing.
The prior art has attempted to overcome the problems associated with the conventional methods for the production of wire and rod by utilizing continuous electrolytic processes whereby a pure copper starting wire is engrossed by passing the wire as a cathode through a tank containing electrolyte and using impure copper or lead as the anode. Many patents have been issued over the years in this area but the need exists for more efficient electrolytic wire making processes and apparatus which are commercially and economically feasible.
U.S. Pat. No. 1,058,048 describes electrodepositing copper onto wire by advancing the wire in a vat of electrolyte in a continuous series of endless travelling loops. U.S. Pat. No. 4,097,354 shows the continuous electrolytic plating of metal using moving cathodes and anodes in the form of sheets or plates. U.K. Patent No. 1,172,906 is directed to producing copper wire by electrodeposition in a continuous process comprising continuously forming an elongated member by electrodeposition on a moving cathode surface, stripping the member from the cathode surface and passing it through electrolyte adjacent to anodes to build up its thickness. U.K. Patent No. 1,398,742 shows a continuous process for electrodepositing copper onto wire by guiding the wire as a cathode through the bath by a plurality of rolls describing any adequate path and, upon emerging from the bath, passing the wire through washing means. U.S. Pat. No. 4,196,059 discloses a method and an apparatus for continuously introducing separate thin copper wires as a cathodic starting or base surface for one pass through a tank for refining impure copper anode blocks thereby engrossing said wires by electrolytic deposition to a large diameter rod (about 20 mm). It is claimed that the process may be operated at high current densities without contamination of the refined rod by the normal impurities found in the anode slime residues.
U.S. Pat. No. 4,395,320 also discloses an electroplating apparatus to engross a wire consisting of a cascade of electrolytic baths separated by rollers pressing on the wire being engrossed in order to smooth its rough surface caused by the high current densities utilized in the process.
U.S Pat. No. 3,676,322 discloses an apparatus and method for continuously producing an electrolytically plated wire which comprises passing a single wire repeatedly in and out of an electrolyte contained in tanks positioned between external guide rolls. The rolls pass the wire continuously through the tanks in a stepwise manner back and forth between the guide rolls with the wire as the cathode and anode electrodes to effect electrolytic plating.
U.S. Pat. No. 4,891,105 shows a method and apparatus for engrossing a single copper wire by passing the wire a plurality of times around electrical conducting external motorized shafts to form at least a pair of wire curtains in the tank. The wire traverses a number of lengthwise passageways a number of times in opposite directions during the engrossing process.
U.S. Pat. No. 3,929,610 shows the electroformation of metallic strands of infinite length by continuous electrodeposition of metal on a conductive strip having a narrow, closed-loop plating surface.
U.S. Pat. No. 4,053,377 is not directed to producing wire and is of interest to show the electrodepositing of copper onto a cathode under conditions of non-turbulent electrolyte flow achieved by means of a venturi section and a single cathode-anode pair.
The disclosures of all of the above patents are hereby incorporated by reference.
While the prior art has made many advances in this art, the need exists for improved methods to commercially produce copper wire and it is an object of the present invention to provide apparatus and processes for effectively and efficiently engrossing large quantities of wire electrolytically.
Other objects and advantages of the invention will be readily apparent from the following description which will be directed for convenience to the engrossment of copper wire with copper.